Exemplary embodiments pertain to the art of gas turbine engines, and more particularly to cooling of gas turbine engine components.
Gas turbines hot section components, for example, turbine vanes and blades and blade outer air seals, inner and outer end walls, combustor panels and other components of the gas turbine engine are configured for use within particular temperature ranges. Often, the conditions in which the components are operated exceed a maximum useful temperature of the material of which the components are formed. Thus, such components often rely on cooling airflow to cool the components during operation. For example, stationary turbine vanes often have internal passages for cooling airflow to flow through, and additionally may have openings in an outer surface of the vane for cooling airflow to exit the interior of the vane structure and form a cooling film of air over the outer surface to provide the necessary thermal conditioning. Similar internal cooling passages are often included in other components, such as the aforementioned turbine blades and blade outer air seals.
Trip strips are often included in the cooling passages, affixed to one or more walls of the cooling passage to increase turbulence of the cooling airflow flowing through the cooling passage, thereby improving heat transfer characteristics of the cooling passage. Currently, there is a limit on how closely spaced the trip strips can be before the heat transfer convective cooling effectiveness of the trip strips decreases. With reduced spacing between adjacent trip strip features, the thermal boundary layer separation and reattachment location no longer occurs between adjacent streamwise trip strip features. Experimental tests have been performed to measure and quantify the internal convective heat transfer augmentation and pressure loss characteristics associated with various trip strip arrays. Extensive design of experiments were performed to evaluate the impact of trip strip geometry shape, orientation, trip strip pitch, trips strip height, for various cooling passage geometries, aspect ratios, shapes, and orientations. Test results identified the optimal trip strip spacing and location of boundary layer reattachment necessary to achieve the highest internal convective heat transfer augmentation. As the streamwise distance between adjacent trips strips is reduced the boundary layer separation and reattachment location becomes sub-optimal in that the reattachment may occur at a location approximately coincident with the adjacent downstream trip strip location. In this respect the relative spacing of the trip strip geometry features has a significant impact on the local vorticities within the thermal boundary layer adjacent to the hot external wall. As the steam-wise trip strip spacing is reduced, the periodicity of the local flow field and subsequent near wall vortex structures associated with the “tripping” of the thermal boundary layer and subsequent flow separation and reattachment becomes compromised. In this sense, reduced streamwise trip strip spacing significantly weakens the near wall turbulence intensity and subsequently lowers the relative convective heat transfer augmentation achievable. In an effort to maximize convective heat transfer augmentation and internal rough wall surface area, it becomes desirable to reduce the streamwise spacing of the trip strip geometry features without compromising the optimal heat transfer augmentation and pressure loss.